1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to methods and apparatus for electrically probe testing a semiconductor chip.
2. Description of the Related Art
Soft defect isolation techniques are critical to the development and manufacture of large-scale integrated circuits such as processors. Examples of such techniques include those methodologies which exploit induced voltage alterations, such as Thermally Induced Voltage Alteration (“TIVA”), Light Induced Voltage Alteration (“LIVA”) and Charge Induced Voltage Alteration (“CIVA”). The basic setup for these techniques uses a constant current source for biasing the device under inspection (“DUT”) and a detector to sense the change in the voltage demand due to the localized heating, light stimulation by the laser or charge stimulation by an e-beam.
The aforementioned conventional stimulation/perturbation techniques can narrow the location of a soft defect down to perhaps a few square microns. To narrow down a defect location ever further and perhaps determine a particular cause of the soft defect, electrical probing is often used. In one conventional technique, a die is placed contact side up on a stage and several probe styluses are brought into contact with those contacts in the vicinity of the location of the soft defect determined by the stimulation/perturbation technique. The probe styluses are operable to sense electrical characteristics associated with the conductor structures, for example a voltage, a current or the presence or absence of continuity. Multiple areas are probed in this way in an attempt to identify a circuit structure that is clearly non-conforming.
One difficulty associated with the conventional stylus electrical probe system is that the differences in electrical behavior between a passing circuit structure and one which has a soft defect may be quite subtle. Indeed, the differences may be so small that they are washed out by noise levels in the testing apparatus. In this basic setup, no external stimulus is applied to the circuits undergoing probing that might cause a soft defect to stand out.
One conventional probe tester does incorporate a heated stage to apply thermal stimulation on a global basis to the backside of the chip while the contact side is electrically probed. The difficulty here is that the stimulation is applied to the backside of the chip and without the ability to focus on a particular location. This type of tester may not be able to resolve subtle soft defects.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.